JP2005517284A - Optical amplifier that pumps multiple wavelengths - Google Patents

Abstract

An optical amplifier according to the present invention includes a substrate, an optical multiplexer embedded in the substrate, a plurality of multi-wavelength pump light sources connected to the optical multiplexer, and an amplification waveguide connected to the optical multiplexer. Is provided. In certain embodiments, the optical signal is directed to another waveguide in the substrate. In another form, a rare earth element is added to the amplification waveguide.

Description

  The present invention relates to the field of optical signal amplification. In particular, the present invention relates to amplification of an optical signal using pumping beam light having a plurality of wavelengths.

  By adding a rare earth element such as erbium together with a plurality of ions, the waveguide can serve as an optical amplifier. The optical signal propagating in the waveguide is amplified when the pumping beam light is introduced. For example, erbium ions are excited to a higher energy state by a pumping beam having a wavelength of about 980 nm or about 1480 nm, and a wide wavelength band of about 1530 nm to 1600 nm as they transition to a lower energy state Amplifies the optical signal. This technique is widely known in optical fiber amplification.

  FIG. 1 is a schematic diagram showing an example of a conventional method for amplifying an optical signal 10 in a planar waveguide 20. The waveguide 20 is embedded in the substrate 30 and erbium ions are added. The optical signal 10 is guided to the waveguide 20 and propagates in the waveguide 20. The pump laser 50 supplies the pumping beam light to the waveguide 20 so as to have the same propagation direction, that is, substantially the same direction as the direction in which the optical signal propagates. The signal 10 and the pump laser 50 are connected to the same waveguide 20 in a temporary directional coupler, for example. In one form, the optical signal 10 having a wavelength of about 1550 nm is amplified by the pump laser 50 providing pumping beam light having a wavelength of about 980 nm, or a wavelength of about 1480 nm.

  FIG. 2 is a schematic diagram showing another example of a conventional method for amplifying the optical signal 10. In FIG. 2, the pump laser 50 is guided from the opposite end of the waveguide 20 to the pumping beam light in the opposite propagation direction, that is, in a direction substantially opposite to the direction in which the optical signal propagates. As in FIG. 1, the optical signal is amplified in the waveguide 20 and output from the substrate 30.

  Current optical networks use single-mode optical fibers for long-distance transfers. This prevents chromatic dispersion, that is, signal attenuation due to the dependence of the speed of light on wavelength. For an effective communication system using a single mode fiber, all optical devices including the fiber and the waveguide amplifier are effectively a single mode system. Due to the conservation of light quantity, which is a universal principle in optics, the light intensity in a single mode cannot be increased simply by using a linear passive (non-energy) optical element. This results in the fact that the intensity of light at a certain wavelength due to only one mode can be coupled into a single mode waveguide. In other words, in an amplifier, only a pump laser having a certain wavelength is allowed to supply pumping beam light in each propagation direction and each polarization direction.

  The optical signal gains gain in the optical amplifier when the intensity of the pumping beam light is above a certain threshold that depends on the intensity of the optical signal and the material properties of the optical amplifier. In order to achieve a sufficiently high amplification factor, the intensity of the pumping beam light must be much higher than this threshold value. As a result, a high power pumping laser is usually required.

  Compared to the invention described below, the above method has several drawbacks. First, the relatively high power lasers used in the same and opposite directions described above are expensive. Second, high power lasers have high energy losses and can cause thermal problems when sealing them. Third, the reliability of high power lasers is generally not as good as that of low power lasers.

  An apparatus and method for amplifying an optical signal using pump light beams of multiple wavelengths is disclosed. A number of low power light sources provide pumping beam light. In some embodiments, a plurality of laser diodes provides this pumping beam light to an optical multiplexer where all the pumping beam light is collected. The optical multiplexer is connected to an optical waveguide where the optical signal is amplified. The combined optical signal and pumping light beams having a plurality of wavelengths are guided to the amplification waveguide, where the optical signal is amplified.

  FIG. 3 is a schematic diagram illustrating an embodiment of optical amplification using multiple-wavelength pump beam light. In an embodiment, the optical amplifier 108 includes a device substrate 105, and the device substrate 105 has a non-added portion 112 and an added portion 114. In some embodiments, rare earth elements such as erbium are used as additives. However, other additives may be used to provide the desired amplifier.

  The optical signal 118 is input through the waveguide 120 embedded in the device substrate 105. When processing and embedding a waveguide in a substrate, there are various methods such as diffusion of various ions, etching, and epitaxial growth. And “embedded in the substrate” means to include these various methods including SOI (Silicon On Insulator). In some cases, the waveguide is actually deposited on top of the substrate and may be covered by a different cladding material than the substrate, but in such cases the term “embedded in the substrate” is also used. include.

  In some embodiments, the arrayed waveguide grating serves as the optical multiplexer 122. In other forms, an eschel diffraction grating serves as the optical multiplexer 122. In some embodiments, the waveguide 120 and the optical multiplexer 122 are temporarily connected to each other at intervals up to several microns. In another form, the waveguide 120 is connected to an amplification waveguide 130, and the amplification waveguide 130 has multiplexed pump beam light after being multiplexed together.

  When the optical signal 118 is connected to multi-wavelength pumping beam light, a plurality of collected light beams coexist in the amplification waveguide 130. In an embodiment, the waveguide 120 and the optical multiplexer 122 are provided in the non-added portion 112 in the device substrate, and the amplification waveguide 130 is provided in the added portion 114 in the device substrate.

  In some embodiments, the plurality of laser diodes 140 provide pumping light beams of a plurality of wavelengths concentrated near the base wavelength. For example, the plurality of laser diodes supply pumping beam light having a small fluctuation amount that is concentrated in the vicinity of 980 nm. Here, the pumping beam light concentrated in the vicinity of 980 nm having a fluctuation amount of 2 nm includes light of 980 nm, 980 ± 2 nm, 980 ± 4 nm, and the like.

  Each variation from the central wavelength need not be periodic or the same, but if one wavelength is too close to another, the output at that wavelength will be In, because of the light quantity conservation law, it is not efficiently transferred to the amplification waveguide. For example, if the output is P and four light sources having the same wavelength are multiplexed into the amplification waveguide, the total amount of output transferred to the amplification waveguide is approximately P (with some loss). It is. The output of about 3P is reflected or scattered. On the other hand, if the output is P and the four light sources have slightly different wavelengths, the total amount of output transferred to the amplification waveguide is approximately 4P (with some loss).

  In some embodiments, a plurality of vertical cavity lasers (VCSELs) are used to provide pump beam light. Here, multiple low-power VCSELs may be used for amplification. For example, one VCSEL may emit light of 20 mW or less, but is not limited to this. The relatively high power laser used in each of the same propagation direction structure and the opposite propagation direction structure shown in FIGS. 1 and 2 is not limited to this, for example, 100 mW. High power laser is used. By using a plurality of VCSELs having slightly different wavelengths, the outputs of each VCSEL are summed together as shown in connection with FIGS. 6, 7, 8 (a), 8 (b).

  FIG. 4 is a schematic diagram showing a second embodiment of optical amplification using a pumping light beam with multiple wavelengths. In the present embodiment, the plurality of light sources 142 supply pumping beam light in the propagation direction opposite to the optical signal 118.

  The optical signal 118 is input to the amplification waveguide 130, and the amplification waveguide 130 exists in the addition portion 114 in the device substrate 105. The plurality of light sources 142 supply pumping beam light equivalent to the plurality of light sources 140, as already described in FIG. The pump beam light is collected in the optical multiplexer 124 and then directed to the amplification waveguide 130 where the optical signal 118 is amplified. In one embodiment, erbium is added to the adding portion 114, the optical signal is about 1550 nm, and the pumping beam light is concentrated around about 980 nm or about 1440 nm.

  In one form, the output waveguide 160 is temporarily connected to one end of the amplification waveguide 130 and the amplified signal is transferred to the output waveguide 160.

  Similar to FIG. 3, the device substrate 105 includes a non-added portion 116 and an added portion 114. In one form, the output waveguide 160 and the optical multiplexer 124 are installed inside the non-added portion 116 in the device substrate 105.

  FIG. 5 is a schematic diagram showing a third form of the optical amplifier 110 in which multi-wavelength pumping beam lights in the same propagation direction and in the opposite propagation directions described in FIGS. 3 and 4 are coupled. This embodiment includes a device substrate having non-addition parts 112 and 116 and an addition part 114.

  The optical signal 118 is input to the waveguide 120, and the waveguide 120 is temporarily connected to the amplification waveguide 130. The plurality of light sources 140 supply pumping light beams having a plurality of wavelengths to the optical multiplexer 122 connected to the amplification waveguide 130, and the plurality of light sources 142 supply a plurality of light to the optical multiplexer 124 connected to the amplification waveguide 130. A pumping beam light having a wavelength of 1 is supplied.

  The optical signal 118 is amplified in the amplification waveguide 130, connected to the waveguide 160, passes through the output waveguide 160, and is output from the device substrate 105.

  3, 4, and 5, various waveguides 120, 130, and 160, and optical multiplexer 122 and optical multiplexer 124 (for example, an arrayed waveguide diffraction grating and an eschel diffraction grating) are respectively included in device substrate 105. For example, it may be formed by various different methods by a known method such as diffusion of various ions, etching, and / or epitaxial growth. For example, in some embodiments, a glass substrate may be used, in which case ion diffusion may be used to create a waveguide in the glass substrate. Furthermore, as is well known, the added portion in the device substrate 105 may be melted together with the non-added portion in the device substrate 105 prior to diffusion. In other forms, a silicon substrate may be used. Silicon oxide is deposited as a cladding and etching may be used to remove this non-waveguide material. The upper cladding, i.e. silicon oxide, may be deposited on top of the waveguides 120, 130, and 160.

  In one form, the plurality of light sources 140 and 142 are connected to the optical multiplexers 122 and 124 via optical fibers (not shown). In another form, the plurality of light sources 140 and 142 are directly connected to the device substrate 105.

  Further, in some embodiments, the plurality of light sources 140 provide a first set of pumping beam lights concentrated around the first wavelength, and the plurality of light sources 142 has a first wavelength different from the first wavelength. A second set of pump beam light concentrated around the two wavelengths may be provided.

  FIG. 6 is an example of a graph corresponding to FIG. 3 illustrating how the optical signal output 210 increases along the length of the amplification waveguide 130 based on the optical pumping 220. In one form, the plurality of light sources 140 provide an output above a certain special threshold Pth in order to obtain a gain. The number and output of the plurality of light sources 140 are set so that the total pump output at the end of the amplification waveguide is greater than or equal to the threshold value Pth and amplification through the total extension of the amplification waveguide 130 is achieved. Is done. Even if each of the plurality of low-power laser diodes supplies pumping beam light that is significantly inferior to the gain threshold value Pth, by combining the pumping beam light of a plurality of wavelengths, the output of the optical signal is , Get high output. As described above, a low-power laser diode generally has the advantages of being inexpensive and highly reliable compared to a high-power laser diode.

  FIG. 7 is an example of a graph corresponding to FIG. 4 illustrating how the optical signal output 230 increases along the length of the amplification waveguide 130 based on the optical pumping 240. The optical signal 118 is amplified even when the pumping beam light is supplied in the anti-propagation direction.

  FIG. 8A and FIG. 8B are examples of graphs corresponding to FIG. 55, showing how the optical signal increases along the length of the amplification waveguide 130. FIG. 8A shows the outputs 250 and 252 of the plurality of pumps 140 and 142 supplied at each end of the amplification waveguide 130 and the respective reductions in the amplification waveguide. FIG. 8B shows how the output of the optical signal 260 increases. As can be seen from the graph, a higher amplification factor is generated at each end of the amplification waveguide where the output of the pumping beam light is maximized.

  Thus, an apparatus and method for amplifying an optical signal has been disclosed. However, only a special configuration and method are shown here. For example, there are various methods for processing a waveguide in a substrate, such as ion species diffusion, etching, and epitaxial growth methods. Those skilled in the art may use any of a variety of techniques, for example, to fabricate an embedded waveguide. Various changes in shape and details can be made without departing from the scope of the present invention defined by the claims. The present invention is limited only by the appended claims.

It is the schematic which shows an example of the conventional method of amplifying the optical signal in a planar waveguide. It is the schematic which shows the other example of the conventional method which amplifies an optical signal. FIG. 6 is a schematic diagram illustrating an embodiment of optical amplification using multi-wavelength pump beam light. It is the schematic which shows 2nd embodiment of optical amplification using the pumping beam light of multiple wavelengths. It is the schematic which showed the 3rd form in the optical amplifier 110 which connected the multi-wavelength pumping beam light in the same propagation direction and the opposite propagation direction. It is an example of the graph which showed a mode that the optical signal output increased based on optical pumping. FIG. 5 is an example of a graph corresponding to FIG. 4 showing how the optical signal output increases along the length of the amplification waveguide based on optical pumping. FIG. 6 is an example of a graph corresponding to FIG. 5 illustrating how an optical signal increases along the length of an amplification waveguide. (A) shows the output of the multiple pumps supplied at each end of the amplification waveguide and the reduction of the output in the amplification waveguide. (B) shows an increase in the output of the optical signal.

Claims (25)

A substrate,
An optical multiplexer embedded in the substrate;
A plurality of pump light sources for multiple wavelengths connected to the optical multiplexer;
An amplification waveguide connected to the optical multiplexer;
An optical amplifier comprising:   The optical amplifier according to claim 1, wherein a rare earth element is added to the amplification waveguide.   The optical amplifier according to claim 1, wherein each of the plurality of pump light sources includes a plurality of laser diodes.   4. The optical amplifier according to claim 3, wherein the plurality of laser diodes are vertical cavity lasers having an output of about 20 mW or less.   The optical amplifier according to claim 1, wherein the optical multiplexer is an arrayed waveguide diffraction grating.   The optical amplifier according to claim 1, wherein the optical multiplexer is an eschel diffraction grating.   The optical amplifier according to claim 1, further comprising a signal waveguide connected to the amplification waveguide and embedded in the substrate. A method of amplifying an optical signal,
A pumping beam light generating step for generating a pumping beam light including a plurality of wavelengths;
An optical waveguide step for guiding the optical signal and the pumping beam light to a planar waveguide doped with a rare earth element;
An optical signal amplification method comprising:   9. The optical signal amplification method according to claim 8, further comprising a pumping beam optical multiplexing step of multiplexing the pumping beam light into a single mode waveguide.   The optical signal amplification method according to claim 8, further comprising a connection step of temporarily connecting the optical signal and the pumping beam light.   9. The optical signal amplification method according to claim 8, wherein the pumping beam light is multiplexed by using an arrayed waveguide diffraction grating.   9. The optical signal amplification method according to claim 8, wherein the pumping beam light is multiplexed by using an echelle diffraction grating.   9. The optical signal amplification method according to claim 8, wherein the pumping beam light is generated by using one or more vertical cavity lasers having an output of about 20 mW or less.   The optical signal amplification method according to claim 8, wherein the optical waveguide step further includes a step of guiding the optical signal and the pumping beam light to a planar waveguide doped with erbium.   The optical signal amplification method according to claim 14, wherein the optical signal has a wavelength of about 1550 nm, and the pumping beam light is concentrated at a wavelength of about 980 nm, or a wavelength of about 1480 nm.   The optical signal amplification method according to claim 15, wherein the pumping beam lights are generated at wavelengths different from each other by an interval of about 2 nm.   The optical signal amplification method according to claim 8, wherein the connecting step temporarily connects the optical signal to the pumping beam light propagating in the same direction as the optical signal.   The optical signal amplification method according to claim 8, wherein the connecting step temporarily connects the optical signal to the pumping beam light propagating in a direction opposite to the optical signal. A first waveguide embedded in the device substrate for transmitting an optical signal;
An optical multiplexer connected to the first waveguide;
Two or more diode lasers for supplying beam lights of different wavelengths to the arrayed waveguide grating;
An optical amplifier including an amplification waveguide to which an erbium element is added, which is connected to the arrayed waveguide diffraction grating and amplifies the optical signal.   20. The optical amplifier according to claim 19, wherein each of the plurality of laser diodes is a vertical cavity laser having an output of about 20 mW or less.   21. The optical amplifier according to claim 20, wherein each of the plurality of laser diodes supplies light beams concentrated at about 980 nm and different from each other by about 2 nm.   21. The optical amplifier according to claim 20, wherein each of the plurality of laser diodes supplies beam light concentrated at about 1480 nm and different from each other by about 2 nm.   20. The optical amplifier according to claim 19, wherein the first waveguide is connected to the arrayed waveguide grating for a predetermined time.   The optical amplifier according to claim 19, wherein the device substrate is phosphate glass.   The optical amplifier according to claim 19, wherein the device substrate comprises silicon dioxide and silicon.

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